Report on WCPFC project 107b: Improved stock assessment and structural uncertainty grid for Southwest Pacific blue shark

This analysis presents additional work in order to constrain the model grid employed for the 2021 south Pacific blue shark (BSH) stock assessment in the Western and Central Pacific Ocean (WCPO). The 2021 stock assessment for BSH was accepted by the Scientific CommiĴee at SC17. However, due to a number of uncertainties about the relative merit (model fit, plausibility) of individual models within the large (3888) model grid, SC17 was hesitant about using such a large grid to provide management advice. The SC17 recommended improving the manner in which the grid was selected before approving the results for providing management advice. The present analysis aĴempted to address these concerns by running a number of standard diagnostics across all grid model runs to ensure that:
1. models had sufficiently converged and results were robust to jiĴering of starting values;
2. models were consistent and did not show large retrospective paĴerns (as evidenced by Mohn’s p); and
3. models had reasonable predictive skill.